Hi Lizzy,
I am so, so sorry. Is he packing his sorry butt up and preparing to move back to the US? I'm just thinking about your emotional state right now and what you said about feeling stuck with him.
I was reading this link that mapleleafgirl72 provided:
http://travel.state.gov/law/info/marriage/marriage_641.html
and this part jumped out at me (emphasis mine):
RECOGNITION BASED ON COMITY: A divorce decree issued in a foreign country generally is recognized in a state in the United States on the basis of comity (Hilton v. Guyot, 159 U.S. 113, 163-64 (1895), provided both parties to the divorce received adequate notice, i.e., service of process and, generally, provided one of the parties was a domiciliary in the foreign nation at the time of the divorce.
I'm not a legal professional, but to me, that sounds like for you to divorce in the UK, at least one of you would have to have UK permanent residency, which neither of you have. Therefore, it sounds like you would need to file in the US state you're resident in. I would start by contacting a divorce attorney in your state. They almost always give free initial consultations, and I'm sure they could do it on the phone. They can explain the process for you - whether you need to be physically present to file, whether your state has any pre-divorce mediation requirements, etc.
If I recall correctly, you have a Tier 2 visa, and he is here as your dependent. The good news in all of this is that your work visa is still valid, so you can continue to live in the UK for its duration. His visa, however, is dependent on his relationship to you, so once you have separated, it is no longer valid, and he must return home.
Big, big hugs to you. Please let us know how you're doing.